如何优化使用游标的PL/SQL代码

-- 示例：使用BULK COLLECT和FORALL
DECLARE
  TYPE emp_tab IS TABLE OF employees%ROWTYPE;
  emp_rec emp_tab;
BEGIN
  SELECT * BULK COLLECT INTO emp_rec FROM employees WHERE department_id = 10;
  
  FORALL i IN 1..emp_rec.COUNT
    UPDATE employees SET salary = salary * 1.05 WHERE employee_id = emp_rec(i).employee_id;
END;

DECLARE
  CURSOR c_emp IS SELECT * FROM employees;
  emp_rec employees%ROWTYPE;
BEGIN
  OPEN c_emp;
  LOOP
    FETCH c_emp INTO emp_rec;
    EXIT WHEN c_emp%NOTFOUND;
    -- 处理数据
  END LOOP;
  CLOSE c_emp; -- 确保关闭游标
END;

-- 示例：使用索引和减少数据提取量
CREATE INDEX idx_dept_id ON employees(department_id);

DECLARE
  CURSOR c_emp IS SELECT employee_id, salary FROM employees WHERE department_id = 10;
  emp_rec c_emp%ROWTYPE;
BEGIN
  OPEN c_emp;
  LOOP
    FETCH c_emp INTO emp_rec;
    EXIT WHEN c_emp%NOTFOUND;
    -- 处理数据
  END LOOP;
  CLOSE c_emp;
END;